MySQL不要两次选择相同的ID

Question

I'm working on a message system, and i can't figure this out! The message system is built up something like this,

ID
MESSAGE_ID
MESSAGE
FROM_USER
TO_USER

The message_id can be the same multiple times, thats the ID the from and to users are reading from while checking messages (so they can see all the messages that has been written). But, i need to select all the messages, but i want to skip a row, if the ID has been select before. Is this possible in MySql? or do i need to run a array then remove all duplicated id's?

Answer 1

SELECT `ID`, `MESSAGE_ID`, `MESSAGE`, `FROM_USER`, `TO_USER`
FROM `YourDbTable`
GROUP BY `ID`, `MESSAGE_ID`

Group By may be what you are looking for...

Answer 2

您可以使用group by message_id

Answer 3

Maybe you can try something like this -

SELECT    DISTINCT (message_id), message, id, 
          from_user, to_user
FROM      test
GROUP BY  message_id
ORDER BY  id; 

A live demo is given here .